'Planet killer' asteroid hidden by the sun may threaten Earth in a few thousand years

• Astronomers discovered a "planet killer" asteroid that may pose a threat to Earth in future millennia.
• The discovery highlights a dangerous blind spot: it's hard to see anything coming from the direction of the sun.

Astronomers discovered a large asteroid nearby this year, on a trajectory that could take it dangerously close to our planet in the distant future.

The asteroid, called 2022 AP7, is about 1.5 kilometers wide — nearly one mile. That makes it a "planet killer," Scott S. Sheppard, an astronomer at the Carnegie Institution for Science, said in a press release announcing the discovery on Monday.

Although the rock isn't as big as the one that led to dinosaurs' extinction, it's big enough to wreak planet-wide destruction and potentially change life on Earth as we know it.

Thankfully, 2022 AP7 isn't headed for Earth anytime soon, especially not in the next century, according to researchers' calculations.

"Way down the line, in the next few thousand years, it could turn into a problem for our descendants," Alan Fitzsimmons, an astronomer at Queen's University Belfast who was not involved in the study, told The New York Times.

But there could be other planet killer asteroids lurking unseen in the blind spot where 2022 AP7 was discovered: within the orbits of Earth and Venus, between us and the sun.

The sun's glare could conceal dangerous asteroids

In August 2020, an asteroid the size of a car passed closer to Earth than any known space rock had ever come without crashing. It missed our planet by about 1,830 miles.

Astronomers didn't know the space rock existed until about six hours after it whizzed by. Nobody saw it coming, because it was approaching from the direction of the sun.

Telescopes spot asteroids by detecting sunlight reflecting off of them. That makes it very difficult to spot asteroids located between Earth and the sun. The brilliant glare of our star — which is 109 times wider than Earth — easily drowns out the faint glint of a mile-wide asteroid. Plus, some asteroids aren't very reflective.

To find more asteroids in this blinding zone, Sheppard's team used a camera designed to detect dark energy, mounted on a telescope at Cerro Tololo Inter-American Observatory in Chile.

They could only scan the near-sun sky during a 10-minute window at twilight, peering at the horizon just before the sun emerges. Sheppard's team was able to identify three previously unknown near-Earth asteroids, including 2022 AP7. The survey results were published in The Astronomical Journal on September 29.

"There are likely only a few [near-Earth asteroids] with similar sizes left to find," Sheppard said in the release.

He added that most of the undiscovered asteroids probably stay closer to the sun, rather than coming near Earth's orbit.

NASA is making Armageddon plans

NASA is working on a game plan for the day scientists detect an asteroid on a true collision course with Earth. The agency just slammed a spacecraft into a distant asteroid and successfully changed that asteroid's orbit around a larger space rock.

That mission, called the Double Asteroid Redirection Test (DART), was practice for striking any asteroid approaching Earth, giving it a nudge to steer it off course. No such asteroids have been identified, but NASA is preparing for the possibility of future discoveries.

However, scientists previously told Insider that NASA would probably need about five to 10 years to build and launch a DART-like deflection mission for an asteroid that posed a threat to Earth. That means astronomers must identify asteroids long before they approach our planet.

NASA is slowly advancing a space telescope to track down more city killer asteroids in our cosmic neighborhood. That project, called the Near-Earth Object (NEO) Surveyor, recently had its budget cut by more than $100 million. It's set to launch as early as 2028.

The telescope is designed to help NASA fulfill a Congressional mandate to find and track 90% of all near-Earth objects 140 meters (460 feet) or larger in size. That's big enough to obliterate a city like New York. The goal was to find them by the end of 2020. Obviously, NASA is behind.

So far, NASA estimates it has only catalogued 40% of those city killers. NEO Surveyor would help spot the rest of them. That includes asteroids coming from the direction of the sun.